Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $87.61   10.424%   $96.7425   $96.74   $96.75   $96.70  
  Purchase #2 $178.60   13.792%   $203.2325   $203.23   $203.25   $203.20  
  Purchase #3 $161.61   6.650%   $172.3571   $172.36   $172.35   $172.40  
  Purchase #4 $170.66   6.644%   $181.9987   $182.00   $182.00   $182.00  
  Purchase #5 $227.78   8.630%   $247.4374   $247.44   $247.45   $247.40  
  Purchase #6 $41.36   8.371%   $44.8222   $44.82   $44.80   $44.80  
  Purchase #7 $187.71   13.639%   $213.3118   $213.31   $213.30   $213.30  
  7 purchase totals = $1,055.33       $1,159.9022   $1,159.90   $1,159.90   $1,159.80